1. Field of the Invention
The present invention relates to a carbon fiber sheet, an arrow shaft and an arrow, and in particular, relates to a carbon fiber sheet, an arrow shaft and an arrow having different spine strengths in the longitudinal direction of the arrow shaft.
2. Description of the Related Art
FIG. 1 is a schematic view of a conventional general arrow, and FIG. 2 is a conceptual view for explaining a flight phenomenon of the arrow.
An arrow 10 is generally comprised of a hollow cylindrical arrow shaft 11, an arrowhead 12 to be mounted to the front end of the arrow shaft 11, a notch 13 to be mounted to the rear end of the arrow shaft 11, and fletchings 14 to be mounted to the rear outer circumferential surface of the arrow shaft 11.
In general, an arrow leaving a bow string is subject to an impellent force which is derived from the power of the bow string pulling a rear end of the arrow. The arrow flies when the impellent force is transmitted to the front of arrow. When the arrow leaves the bow string and flies toward a target, the arrow suffers a flight phenomenon. The flight phenomenon occurs an early stage of flying shortly after leaving the bow wherein the arrow flies while shaking mainly from side to side.
In shooting an arrow, or when the arrow leaves the string, kinetic energy is momentarily transferred to the arrow. Due to such energy, the arrow is subject to bending at a pressure point and the bending dissipates to the original state of the arrow thanks to the elastic body of arrow shaft, and yet bends again in the opposite direction due to inertial energy. All the while, the arrow keeps flying while repeating such phenomena until the inertial energy is extinguished.
However, in the case of arrows for archery, the arrows are shot dozens to hundreds of times a day, so the flight phenomenon has detrimental effects on the arrow shafts. That is, as shown in FIG. 2, the arrow shaft while flying is subject to repeated bending, interchanging directions at a pressure point (i.e., center of gravity). In cases where the arrow shaft continually undergoes such a phenomenon, the arrow shaft may be subject to deformation or damage in the front or middle parts of the arrow where the center of gravity in the arrow shaft is positioned.
In order to overcome such problems, an arrow shaft was proposed with a configuration wherein a hollow aluminum tube is disposed as a core within an inner portion, and a carbon fiber sheet is laminated on the outer portion of the aluminum tube to form a double layer, then the front and rear portions of the carbon fiber sheet layer are ground with a grinding machine yielding a thicker middle portion of the arrow.
However, such an arrow product has problems wherein as the diameter of the arrow shaft is adjusted during the grinding of the carbon fiber sheet layer, it becomes difficult to manage dimensional control, the internal structure of the sheet layer is sensitive to processing defects during the grinding, and hence the arrow shaft is prone to be eccentric due to lacking exact dimensional control. In addition, it is difficult to join the aluminum core and the carbon fiber sheet layer together, and as the aluminum tube is disposed in the inner portion, the weight of the arrow shaft is increased. Further still, as the front and rear outer circumferential surfaces of the arrow shaft are ground to their required diameters, resulting in wasted material, the processing times required for machining become longer, resulting in lower productivity.
Yet further still, there is a disadvantage wherein the carbon fiber sheet layer may be peeled off or stripped off from the aluminum tube due to the impact of the arrow shaft or the different coefficients of thermal expansion between the two different materials.
As described above, the flight phenomenon occurs from the moment when the arrow is shot from the bow. At this time, if the strength, weight, and length, etc. of the arrow shaft, with respect to the strength of bow, are not appropriately considered, the arrow will not be able to fly straight.
In general, the meaning of a strong waist force is when the strength of the arrow is stronger compared to the strength of the bow (i.e., the waist force of the arrow is strong), and the meaning of a weak waist force is when the strength of the arrow is weaker compared to the strength of the bow. Therefore, in order to measure the strength of the arrow shaft, a weight is applied at the center of the arrow shaft and the amount of bending of the arrow shaft is measured. With this measurement, an arrow shaft appropriate to the strength of the bow is selected. Here, the amount of bending is in reference to the spine of the arrow.
A larger spine of the arrow shaft may provide straighter arrow flight, or less deformation of the material of which the arrow is made from caused by the frequent flight phenomenon (supra). However, the spine of the arrow must be determined in consideration of the strength of the bow. Therefore, it is not always unconditionally advantageous to make the spine larger, and furthermore, larger spines require higher material and manufacturing costs.
In addition, an arrow shaft may be subject to different external forces depending on certain positions in the longitudinal direction of the arrow shaft. More specifically, the middle portion of the arrow shaft is prone to be weakened due to the frequent bending forces caused by the above mentioned flight phenomenon, the front portion of the arrow shaft coupled with an arrowhead typically receives the most impact when the arrow strikes the target during frequent shooting, and the rear portion of the arrow shaft coupled with the notch typically receives the most impact from the string.
As described above, the arrow shaft typically receives different impact forces depending on its physical properties, size, and the respective locations along the longitudinal length of the arrow shaft. Therefore, it is necessary to differentiate elasticity, strength, or other properties in the longitudinal direction of the arrow shaft. Further, it is necessary for elasticity, strength, or other properties in the longitudinal direction of the arrow shaft to be stably secured, even though the arrow shaft may be bent due to errors in the manufacturing process and/or flight phenomenon.